Christian Gomez, 23, also told authorities that he had committed the murder because he felt his mother favored his brother over him.
"In a very calm, cool way, he explained what he did, why he did it and what happened and by talking to him, you wouldn't know he had any mental illness... that's very scary," Pinellas County Sheriff Bob Gualtieri told WFLA.
Family members told the station that Gomez had been diagnosed with schizophrenia, and struggled with his illness.
Gomez admitted the killing to police after his brother turned him in last week.
According to the Pinellas County Sheriff's Office, Mario Gomez called 911 on Wednesday evening and told dispatchers that his brother Christian had killed their mother and cut off her head.
Deputies found Maria Suarez-Cassagne's body outside the Oldsmar home, near some garbage cans. Authorities say 23-year-old Christian Gomez had fled the scene, but he was arrested after another 911 call reported a suspicious person riding a bicycle in the area.
Gomez allegedly put his mother's head in a trash can outside, and attempted to drag her body into the garage, but it was too heavy. The suspect's brother, who was home at the time, said he thought it was just the sound of his brother dragging boxes.